Oximeter sensor with digital memory encoding patient data

ABSTRACT

The present invention provides a memory chip for use in an oximeter sensor, or an associated adapter or connector circuit. The memory chip allows the storing of patient related data, such as patient trending data or a patient ID, to provide enhanced capabilities for the oximeter sensor. In addition to providing unique data to store in such a memory, the present invention include unique uses of the data stored in such a memory.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication No. 60/229,616, filed Aug. 31, 2001, which is herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to oximetry sensors and, inparticular, pulse oximetry sensors which include coded informationrelating to patients.

[0003] Pulse oximetry is typically used to measure various blood flowcharacteristics including, but not limited to, the blood-oxygensaturation of hemoglobin in arterial blood, the volume of individualblood pulsations supplying the tissue, and the rate of blood pulsationscorresponding to each heartbeat of a patient. Measurement of thesecharacteristics has been accomplished by use of a non-invasive sensorwhich passes light through a portion of the patient's tissue where bloodperfuses the tissue, and photoelectrically senses the absorption oflight in such tissue. The amount of light absorbed is then used tocalculate the amount of blood constituent being measured.

[0004] The light passed through the tissue is selected to be of one ormore wavelengths that are absorbed by the blood in an amountrepresentative of the amount of the blood constituent present in theblood. The amount of transmitted light passed through the tissue willvary in accordance with the changing amount of blood constituent in thetissue and the related light absorption. For measuring blood oxygenlevel, such sensors have been provided with light sources andphotodetectors that are adapted to operate at two different wavelengths,in accordance with known techniques for measuring blood oxygensaturation.

[0005] An encoding mechanism is shown in U.S. Pat. No. 4,700,708, thedisclosure of which is incorporated herein by reference. This mechanismrelates to an optical oximeter probe which uses a pair of light emittingdiodes (LEDs) to direct light through blood-perfused tissue, with adetector picking up light which has not been absorbed by the tissue. Theoperation depends upon knowing the wavelength of the LEDs. Since thewavelength of LEDs can vary, a coding resistor is placed in the probewith the value of the resistor corresponding to the actual wavelength ofat least one of the LEDs. When the oximeter instrument is turned on, itfirst applies a current to the coding resistor and measures the voltageto determine the value of the resistor and thus the value of thewavelength of the LED in the probe.

[0006] U.S. Pat. No. 5,259,381 recognizes that the coded value of thewavelength of the red LED provided by a coding resistor may beinaccurate, since the actual wavelength can vary with temperature.Accordingly, this patent teaches including a temperature sensor in theoximeter probe to measure the actual temperature. With the actualtemperature, and the coded wavelength value, a look-up table can beconsulted to determine the actual LED wavelength for that temperature.

[0007] Another method of storing coded information regarding thecharacteristics of the LEDs is shown in U.S. Pat. No. 4,942,877 assignedto Minolta. This patent discloses using an EPROM memory to store digitalinformation, which can be provided in parallel or serially from thesensor probe to the remote oximeter. The memory is described as storingcoefficients for the saturation equation, wavelength, subwavelength(where 2 peaks for LED), half-width of wavelength spectrum emitted byLED, intensity of LEDS or ratio, and on time of LEDS (written by theprocessor).

[0008] Other examples of coding probe characteristics exist in otherareas. Multiple calibration values are sometimes required, with thismaking the circuitry more complex or requiring many leads. In U.S. Pat.No. 4,446,715, assigned to Camino Laboratories, Inc., a number ofresistors are used to provide coded information regarding thecharacteristics of a pressure transducer. U.S. Pat. No. 3,790,910discloses another pressure transducer with a ROM storing characteristicsof the individual transducer. U.S. Pat. No. 4,303,984 shows anotherprobe with digital characterization information stored in a PROM, whichis read serially using a shift register.

[0009] Typically, the coding element is mounted in the probe itself. Forinstance, U.S. Pat. No. 4,621,643 shows the coding resistor mounted inthe probe element itself. In addition, U.S. Pat. No. 5,246,003 shows thecoding resistor being formed with a printed conductive material on theprobe itself.

[0010] In some devices, an electrical connector coupled by a cable to adevice attached to a patient may include a coding element. For example,U.S. Pat. No. 3,720,199 shows an intra-aortic balloon catheter with aconnector between the catheter and a console. The connector includes aresistor with a value chosen to reflect the volumetric displacement ofthe particular balloon. U.S. Pat. No. 4,684,245 discloses a fiberopticcatheter with a module between the fiberoptic and electrical wiresconnected to a processor. The module converts the light signals intoelectrical signals, and includes a memory storing calibration signals sothe module and catheter can be disconnected from the processor and usedwith a different processor without requiring a recalibration.

[0011] U.S. Pat. No. 5,645,059 teaches using a modulated signal toprovide the coded data to a remote analyzer. U.S. Pat. No. 5,429,129shows using a voltage regulator to produce a specific voltage value inresponse to an attempt to read by the analyzer.

[0012] Hewlett-Packard Company U.S. Pat. No. 5,058,588 teaches anoximeter sensor with an encoding element that could be resistor, ROM, orcustomized integrated circuit. The encoding element encodes the type ofsensor (in particular, type indicating area of placement on body—finger,ear, foot, arm; also, the type of sensor can indicatetransmission/reflection type, or adult/neonate {indicating correction tobe performed on theoretical oxygen saturation, allow switching betweenphysiological limits such as minimum/maximum pulse rates foradults/neonates}; the maximum driving current may be adapted accordingto type of sensor, and contact of sensor with tissue can be tested bymeans of an attenuation measurement if sensor type is known).

[0013] Nellcor U.S. Pat. No. 5,645,059, the disclosure of which ishereby incorporated herein by reference, teaches coding information insensor memory used to provide pulse modulated signal, to indicate thetype of sensor (finger, nose), the wavelength of a second LED, thenumber of LEDs, the numerical correction terms to the standard curves,and an identifier of the manufacturer.

[0014] A number of catheter patents also discuss encoding information inthe catheter. Sentron U.S. Pat. No. 4,858,615 teaches encoding the typeof sensor, type number, serial number, date of production, safe use lifeof the sensor, correction data for non-linearity, pressure sensitivity,offset, and temperature sensitivity.

[0015] Interflo Medical Published PCT Application No. PCT/US92/08263,Publication No. WO 93/06776 teaches encoding patient specific data,size, manufacture date, batch number, sterilization date, expirationdate, transducer number and type, manufacturer's name and address,thermistor heating element resistance, filament efficiency, programsegments or patient historical data., format version for the calibrationdata, trademark information, catheter unique serial number, ship date,other date and time information, security code to identify manufacturer,thermal mass, filament composition, coefficient of resistance, layoutbyte, checksum, copyright, number of seconds since a certain date,patient weight, patient height, timestamp of 1st CO data point, and acount of all CO data points in EEPROM.

[0016] Dulex-Ohmeda of Boulder, Colo. markets an oximeter sensor productthat encodes data into resistor values representing pointers to a lookuptable containing coefficients (as in U.S. Pat. No. 4,700,708) as well asindicating a range of LED drive current to use with the sensor. The LEDsare driven with a higher or lower drive currents depending upon thevalue of the resistor in a particular sensor.

[0017] Honeywell U.S. Pat. No. 4,303,984 (expires Dec. 14, 1999)describes a memory which stores characterization information, such aslinearization information for a pressure sensor. Alnor Instrument U.S.Pat. No. 5,162,725 describes storing both calibration and ID informationin a sensor memory. Seimans U.S. Pat. No. 5,016,198 describes a codingmemory in a sensor with data for defining sensor's characteristic curve.McBean U.S. Pat. No. 5,365,462 describes a date code in a sensor memory.Honeywell U.S. Pat. No. 4,734,873 describes a pressure sensor with aPROM storing coefficients for a polynomial. Robert Bosch U.S. Pat. No.4,845,649 describes a PROM in a sensor storing correcting data.

[0018] McBean U.S. Pat. No. 5,371,128 relates to EEPROM in sensor withsensor type code and calibration data. McBean U.S. Pat. No. 5,347,476describes an accuracy code. Otax U.S. Pat. No. 5,528,519 shows a PROM ina connector for oximeter.

[0019] Square D Company U.S. Pat. No. 5,070,732 shows calibration datain a sensor memory. Baxter U.S. Pat. No. 5,720,293 talks about differentcalibration information for a catheter, including a security code(encryption is discussed), serial number, model number, ID data such ascalibration, manufacture, sterilization and ship date or other date andtime information, a software program segment, security code foridentifying whether sensor made by same manufacturer as monitormanufacturer, filament or transducer resistance, heat transfercoefficient, thermal mass, filament composition and coefficient ofresistance, layout byte, copyright notice, checksum, random data bytes.Porsche U.S. Pat. No. 5,008,843 describes a sensor with EEPROM ID andcharacteristics data.

BRIEF SUMMARY OF THE INVENTION

[0020] The present invention provides a memory chip for use in anoximeter sensor, or an associated adapter or connector circuit. Thememory chip allows the storing of patient related data, such as patienttrending data or a patient ID, to provide enhanced capabilities for theoximeter sensor. In addition to providing unique data to store in such amemory, the present invention include unique uses of the data stored insuch a memory.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a block diagram of a pulse oximeter system in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022]FIG. 1 is a block diagram of a pulse oximeter system incorporatinga calibration memory element 56 according to the invention. In oneembodiment, memory element 56 is a two-lead semiconductor digital memorychip. The calibration element is part of the sensor 50 which alsoincludes red and infrared LEDs 52 as in the prior art, along with adetector 54. If desired, LEDs 52 may be replaced with other lightemitting elements such as lasers.

[0023] The oximeter includes read circuit 60, drive circuit 66, look-uptables 62 and 63, controller 64, amplifier 72, filter 74, andanalog-to-digital converter 76. Read circuit 60 is provided for readingmultiple coded values across the two leads 51, 53 connected tocalibration element 56. One value is provided to a look-up table 62 todetermine appropriate wavelength dependent coefficients for the oxygensaturation calculation, as in the prior art. The other value(s) are thenprovided to another look up table(s) 63 which provides input (e.g.,coefficients) to other calculations performed by controller 64. Theseadditional calculations may enhance the performance and/or safety of thesystem. Controller 64 provides signals to a drive circuit 66, to controlthe amount of drive current provided to LEDs 52.

[0024] As in the prior art, detector 54 is connected through anamplifier 72 and a filter 74 to an A/D converter 76. This forms afeedback path used by controller 64 to adjust the drive current tooptimize the intensity range of the signal received. For properoperation the signal must be within the analog range of the circuitsemployed. The signal should also be well within the range of A/Dconverter 76. For example, one rule that may be applied is to adjust LEDdrives and amplifier gains so that both red and IR signals fall between40% and 80% of full scale reading of converter 76. This requires correctand independent settings for both the red and infrared LEDs.

[0025] In an embodiment of the present invention, patient-specific datasuch as trending data or patient monitoring parameters can be activelystored in the memory of memory chip 56. As the patient and sensor travelfrom ward-to-ward of the hospital, and consequently plug into differentoximeters, the patient-specific data can be read from memory 56 of thepatient's dedicated sensor and displayed on a display screen for viewingor used by the oximeter monitor for other purposes. Memory 56 may, forexample, be implemented as a random access memory (RAM), a FLASH memory,a programmable read only memory (PROM), an electrically erasable PROM, asimilar programmable and/or erasable memory, any kind of erasablememory, a write once memory, or other memory technologies capable ofwrite operations. Examples of patient specific data that can be storedin memory 56 are now discussed.

[0026] Patient trending data regarding the history of a patient's bloodoxygen saturation (SpO₂) level, pulse rate, pulse amplitude, perfusiondata, and other patient data over a period of time can be recorded inmemory chip 56. The oximeter monitor can continuously or periodicallystore a patient's current trend data into memory 56 to maintain ahistorical data for the patient. The patient trend data can be erasedfrom memory 56 each time a sensor is used on a new patient (e.g., eachtime the oximeter monitor is turned off or when user input to themonitor indicates a new patient). Alternatively, the data encoded intomemory 56 can be permanent and non-erasable. Further details of a Methodand Circuit for Storing and Providing Historical Physiological Data arediscussed in U.S. patent application Ser. No. 09/520,104 to Swedlow etal., filed Mar. 7, 2000, which is incorporated by reference herein inits entirety.

[0027] As another example, the lowest and/or highest blood oxygensaturation level, pulse rate, pulse amplitude value, temperature data,blood pressure, perfusion data, or any other patient data during themonitored time may be stored in memory 56 by the oximeter monitor. Ifdesired, the lowest/highest values of these patient parameters over apast specified monitoring time (e.g., 2 hours, 1 day, etc.) may berecorded in memory 56.

[0028] Expected ranges for patient parameters (such as pulse rate, pulseamplitude, and blood oxygen saturation level) that are specific to aparticular patient may also be recorded in memory 56 by a clinician.This can be a desirable feature, because the expected patient trendingdata can vary significantly for each patient. The oximeter monitor cancompare the expected range for the patient stored in memory 56 with themonitored patient trending data to determine if the patient's pulse andblood oxygen levels are within the expected range for that patient. Ifthe monitored patient parameter varies outside the patient-specificrange recorded in memory 56, a warning message may be displayed on theoximeter monitor or alarm signal may be sounded. If desired, anyvariations in the monitored patient parameters from the expected rangesmay be recorded in memory 56 along with a time stamp.

[0029] If desired, portions of a patient's medical chart and/or pastmedical history can be digitally encoded and stored in memory 56 (ifsufficient memory space is available) so that this information ismaintained with the patient as he is moved around and can be easilyaccessed and displayed using an oximeter monitor if the patienttransferred to a different room or hospital.

[0030] The pulse oximeter can keep track of how long a particularpatient has been monitored by the pulse oximeter and can periodicallystore that time interval in memory 56 by checking the elapsed time on acounter. The counter may be a circuit element in the oximeter monitorthat is reset each time the oximeter monitor begins to receive datasignals from a sensor or each time that the oximeter monitor is turnedoff. The time period that a patient has been monitored by the oximetersensor may be displayed on a display screen for viewing.

[0031] The pulse oximeter monitor may also include a digital clock thatkeeps track of the current date and time. The date and time that theoximeter monitor was turned on and the date and time that the oximetermonitor was turned off may be encoded into the sensor in memory 56. Whenthe oximeter monitor is turned back on again, the monitor can displaythe date and time that it was last turned on and off. It may bedesirable for medical personnel to know the last time that patient'svital signs were monitored by the oximeter.

[0032] The oximeter monitor instrument may also write the alarm limitsused with a particular patient into memory chip 56. Alarm limits arevalues that represent maximum or minimum values of patient trending datatracked by the oximeter (such as blood oxygen saturation, pulse rate,pulse amplitude, etc.) that will trigger an alarm, because they areconsidered to be dangerous levels. The alarm limit values may be encodedin memory 56 by the manufacturer or by a clinician through the oximetermonitor prior to operation.

[0033] The oximeter monitor periodically checks the patient's monitoredtrending data against the alarm limit values. When one of the monitoredpatient parameters reaches the alarm limit value stored in memory 56,the oximeter monitor triggers an alarm which alerts medical personnelthat a problem may exist. The present invention also allowspatient-specific alarm values to be set by medical personnel through theoximeter and stored in memory 56 so that as the patient moves frommonitor-to-monitor (while the sensor stays with the patient), theappropriate alarm limits need not be reset each time on the new monitor.Instead, the alarm limits only need to be programmed once, or at a latertime, whenever the clinician adjusts alarm limits.

[0034] One of more of the patient trending data including blood oxygensaturation, pulse rate, and pulse amplitude can be written to memory 56along with a time of occurrence whenever an alarm threshold is crossed.Additional information, such as the readings for a predetermined timeprior to an alarm occurrence can also be stored, and/or periodic valuesduring the alarm breach can also be stored in memory 56.

[0035] Currently sensors are placed on patients at one hospital site andstay with the patient from hospital site-to-site. It would therefore bedesirable to have a patient identification code (patient ID) such as aunique number carried along in the sensor so that the record keeping,which occurs at each site, can link the recorded information with thepatient. Without a patient ID stored in the sensor itself, the trackinghas to be done manually. This method is prone to mistakes and increasesthe labor involved in managing the patient.

[0036] Thus, in a further embodiment of the present invention theoximeter monitor can store a patient ID in memory 56 of sensor 50. Theoximeter has an input device such as a keyboard, touch screen, orscanner that allows a patient ID to be entered and reentered into theoximeter so that it can be stored in sensor memory 56. With patienttrending information being stored in memory 56 of the sensor asdiscussed above, it is also desirable to have the patient ID stored inmemory 56 so that as the patient goes from hospital location tolocation, the new location's staff can verify that old trendinginformation stored in memory 56 was indeed obtained from that particularpatient. Medical personnel can check that the patient ID stored insensor 50 matches the patient ID on the patient's chart and other paperdocumentation to verify that these medical records correspond to thecorrect patient. If desired, the oximeter sensor can be interfaced witha hospital computer network that maintains a database of patient IDnumbers to verify the identify of the patient and to obtain medicalrecords and other information for the patient stored on hospitaldatabases. The patient ID stored in memory 56 provides assurance thatany data read from memory 56 of the sensor is correlated with thepatient they are receiving.

[0037] The pulse amplitude of the measured photoplethysmogram is anindirect measure of blood perfusion (flow) in the local tissue, changesin blood pressure, vascular tone, vasoconstriction or dilation, forexample, all have an effect on the pulsatile signal strength observedwith a pulse oximeter.

[0038] The measured modulation, or other measurement of perfusion, canbe stored in memory 56 for patient trending purposes. The oximeter cancompare current modulation and perfusion data with older data frommemory 56 to determine patient trends over time. The patient's pulseamplitude deteriorating over time may reflect a serious condition thatdemands attention. Therefore, it is desirable to store and monitorchanges in a patient's perfusion over time. Also, a maximum or minimumperfusion limit may be stored in memory 56 that represents the maximumor minimum value that the patient's measured perfusion can reach beforethe sensor needs to be moved, repositioned, or adjusted in some otherway. The oximeter can trigger a warning signal or light when a perfusionlimit has been reached or a significant change has occurred.

[0039] While the present invention has been described herein withreference to particular embodiments thereof, a latitude of modification,various changes and substitutions are intended in the foregoingdisclosure, and it will be appreciated that in some instances somefeatures of the invention will be employed without a corresponding useof other features without departing from the scope of the invention asset forth. Therefore, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from the essential scope and spirit of the presentinvention. It is intended that the invention not be limited to theparticular embodiments disclosed, but that the invention will includeall embodiments and equivalents falling within the scope of the claims.

What is claimed is:
 1. An oximeter sensor comprising: a light emittingelement; a light detecting element; and a memory device for storingdigital data, said digital data comprising trending data expected for aparticular patient.
 2. The oximeter sensor of claim 1 wherein saidmemory device encodes trending data including blood oxygen saturationdata specific to a patient.
 3. The oximeter sensor of claim 2 whereinsaid memory device encodes a highest and a lowest blood oxygensaturation level monitored during a period of time.
 4. The oximetersensor of claim 1 wherein said memory device encodes trending dataincluding pulse rate data specific to a patient.
 5. The oximeter sensorof claim 1 wherein said memory device encodes a duration of time that apatient parameter decoded from signals received from said lightdetecting element exceeded or fell below the expected trending data. 6.The oximeter sensor of claim 1 wherein said memory device encodes pulseamplitude data for a patient.
 7. An oximeter sensor comprising: a lightemitting element; a light detecting element; and a memory device forstoring digital data, said digital data comprising a patientidentification code.
 8. An oximeter sensor comprising: a light emittingelement; a light detecting element; and a memory device for storingdigital data, said digital data comprising a length of time that apatient has been monitored using the oximeter sensor.
 9. An oximetersensor comprising: a light emitting element; a light detecting element;and a memory device for storing digital data, said digital datacomprising a time when an oximeter monitor coupled to the oximetersensor was turned on or turned off.
 10. An oximeter sensor comprising: alight emitting element; a light detecting element; and a memory devicefor storing digital data, said digital data comprising oximeter alarmlimit values that are patient-specific.
 11. The oximeter sensor of claim10 wherein the alarm limit is a maximum or minimum blood oxygensaturation level.
 12. The oximeter sensor of claim 10 wherein the alarmlimit is a maximum or minimum pulse rate.
 13. The oximeter sensor ofclaim 10 wherein said memory device encodes patient trending data afteran alarm limit value has been reached.
 14. The oximeter sensor of claim13 wherein said patient trending data comprises perfusion data.
 15. Theoximeter sensor of claim 13 wherein said patient trending data comprisesblood oxygen saturation levels.
 16. The oximeter sensor of claim 10wherein said memory device encodes a patient trending data periodicallybefore an alarm limit value has been reached.
 17. The oximeter sensor ofclaim 16 wherein said patient trending data comprises blood oxygensaturation levels.
 18. The oximeter sensor of claim 16 wherein saidpatient trending data comprises blood perfusion data.
 19. The oximetersensor of claim 10 wherein said memory device encodes a time that analarm limit was initially breached.
 20. A method for storing data in anoximeter sensor, the method comprising: emitting light from a lightemitting element; detecting light from the light emitting element usinga photodetector; and storing digitally encoded data in a memory in thesensor, the digitally encoded data including a patient ID; and trackingpatient information using the patient ID.
 21. A method for storing datain an oximeter sensor, the method comprising: emitting light from alight emitting element; detecting light from the light emitting elementusing a photodetector; and storing digitally encoded data in a memory inthe sensor, the digitally encoded data comprising trending data expectedfor a specific patient.
 22. The method of claim 21 wherein storing thedigitally encoded data in the memory further comprises storing anexpected range for blood oxygen saturation levels specific to a patientin the memory.
 23. The method of claim 21 wherein storing the digitallyencoded data in the memory further comprises storing a highest and alowest blood oxygen saturation level for the patient during a period oftime in the memory.
 24. The method of claim 21 wherein storing thedigitally encoded data in the memory further comprises storing anexpected range for patient-specific pulse rate data in the memory. 25.The method of claim 21 wherein storing the digitally encoded data in thememory further comprises storing a length of time that the patient hasbeen monitored using the oximeter sensor in the memory.
 26. The methodof claim 21 wherein storing the digitally encoded data in the memoryfurther comprises storing expected blood perfusion data for the patientin the memory.
 27. The method of claim 21 wherein storing the digitallyencoded data in the memory further comprises storing oximeter alarmlimit values that are patient-specific in the memory.
 28. The method ofclaim 27 wherein storing the digitally encoded data in the memoryfurther comprises storing monitored patient trending data received fromthe photodetector in the memory after one of the alarm limit values hasbeen reached.
 29. The method of claim 27 wherein storing the digitallyencoded data in the memory further comprises storing a time that one ofthe alarm limit values was breached.
 30. The method of claim 27 whereinone of the alarm limit values is a patient specific blood oxygensaturation level.
 31. A method for storing data in an oximeter sensor,the method comprising: emitting light from a light emitting element;detecting light from the light emitting element using a photodetector;and storing digitally encoded data in a memory in the sensor, thedigitally encoded data comprising a time when an oximeter monitorcoupled to the oximeter sensor was turned on or turned off in thememory.
 32. A method for storing data in an oximeter sensor, the methodcomprising: emitting light from a light emitting element; detectinglight from the light emitting element using a photodetector; and storingdigitally encoded data in a memory in the sensor, the digitally encodeddata comprising a duration of time that a patient has been monitoredusing said oximeter sensor.